The present invention relates in general to a system for controlling the rotary drive of a player for recorded disks. More particularly, the invention relates to such a system for a player for video disks recorded with data at a substantially constant packing density.
FIG. 1 is a view of a typical conventional system for controlling the rotary drive of a video disk player. In the drawing, reference numeral 1 designates a CLV (Constant Linear Velocity) disk on which data is recorded in a spiral track using the constant linear velocity method. The disk 1 is driven by a spindle motor 2. A pickup 3 provided above the disk 1 reads the recorded information from the disk. A slider incorporated shift mechanism, no shown, is provided to shift the pickup 3 in a radial direction across the disk 1 as the disk 1 is rotated during reproduction.
The output signals from the pickup 3 are supplied to a signal processing circuit 4 for correction. The signal processing circuit 4 is connected at its output to a reproduced synchronizing signal extracting circuit 5. From the signals output from the signal processing circuit 4, the reproduced synchronizing signal extracting circuit 5 separates the reproduced synchronizing signals and supplies the same to a control signal generating circuit 6. The control signal generating circuit 6 may, for example, be of the type capable of comparing a reproduced synchronizing signal with a reference synchronizing signal and generating a control signal indicative of the result of such comparison. The control signal generating circuit 6 is connected at its output to a drive circuit 8 for driving the motor 2 via a selector switch 7.
A position detector 9 detects the position of the pickup 3 and generates a position signal of a level proportional to the distance through which the pickup 3 has moved from a reference position. The output of the position detector 9 is applied to a divider 10. The divider 10 is connected at its output to the input of a reference voltage generating circuit 11. This reference voltage generating circuit 11 may be composed of, for example, a potential divider which divides the voltage output from the divider 10 and which has three output terminals, each outputting a different voltage magnitude, that is, a first output terminal outputs a voltage level V.sub.a, a second output terminal outputs a voltage level V.sub.b, and a third terminal a voltage level V.sub.c, wherein V.sub.b &lt;V.sub.a &lt;V.sub.c. The first output terminal is connected to a differential amplifier 31 via its negative input terminal. The second output terminal is connected to one input terminal of a comparator 32, and the third output terminal is connected to one input terminal of a comparator 33. Also, a rotary pulse generator 13 is connected to the driving shaft of the motor 2. The pulse generator 13 generates a pulse signal of a frequency proportional to the speed of the motor 2. The pulse generator 13 is connected at its output to an F/V (Frequency/Voltage) converter 14. The voltage output from the F/V converter 14 is supplied to the differential amplifier 31 via its positive input and to the other inputs of the comparators 32 and 33.
The output signals of the comparators 32 and 33 are supplied to a OR gate 34, the output of which controls the position of selector switch 7. The selector switch 7, when in its normal position, passes signals output from the control signal generating circuit 6 to the drive circuit 8, and, in its actuated position, allows signals output from the differential amplifier 31 to be applied to the drive circuit 8.
In the prior art systems for controlling the rotary drive of recorded disks having such a construction, the output signal of the pickup 3 is converted by the signal processing circuit 4 to a desired signal form. From the signals output from the signal processing circuit 4, the reproduced synchronizing signal extracting circuit 5 separates out a synchronizing signal. Based on this synchronizing signal, the control signal generating circuit 6 generates a control signal. The control signal is then passed via the selector switch 7 to the drive circuit 8, which in turns determines the speed of the motor 2 using loop control. Such loop control is utilized when the data of the disk 1 is to be reproduced in a normal manner.
The position detector 9 outputs a voltage signal of magnitude corresponding to the distance through which the pickup 3 has been moved radially across the disk 1. The divider then converts the voltage output to a voltage magnitude representing the reciprocal of the pickup deflected distance.
If the angular speed of the disk to be read is .omega. at a particular point on the disk radially removed from the center thereof by a distance r, the relation of r and .omega. to the linear velocity v is expressed by v=r.multidot..omega.. For a given value of linear velocity v, distance r is inversely proportional to angular speed .omega.. Accordingly, the output voltage of the location detector 9 is proportional to the distance r, and thus the output voltage of the divider 10 is in proportion to 1/r, that is, in proportion to speed .omega.. The three voltages V.sub.a, V.sub.b and V.sub.c produced by the reference voltage generating circuit 11 are based on the output voltage of the divider 10. Specifically, the voltages V.sub.a, V.sub.b and V.sub.c are proportional to the output voltage of the divider 10, and decrease according as the pickup 3 moves closer to the outer circumference of the disk 1, as shown in FIG. 2. The voltage V.sub.a corresponds to the target speed (operating speed) of the motor 2 at a given deflected position of the pickup 3, the voltage V.sub.b corresponds to a lower limit speed smaller than the target speed, and V.sub.c corresponds a upper limit speed greater than the target speed.
The pulse signal output by the frequency generator 13 at a frequency proportional to the speed of the motor 2 is converted by the F/V converter 14 to a voltage signal of magnitude proportional to the frequency of the original pulse signal. The differential amplifier 31 outputs a voltage signal whose magnitude is proportional to the difference between the converted voltage from the converter and the voltage V.sub.a. This converted voltage is also compared by the comparator 32 with the voltage V.sub.b and, when the converted voltage is smaller than V.sub.b, the output level of the comparator 32 becomes high. Moreover, this converted voltage is compared by the comparator 33 with the voltage V.sub.c and, when the converted voltage is greater than V.sub.c, the output level of the comparator 33 becomes high.
Since the output level of the comparator 32 is ORed with that of the comparator 33 by the OR gate 34, when the converted voltage is of a magnitude between V.sub.b and V.sub.c, the output level of the OR gate 34 is low. Either when the converted voltage is smaller than V.sub.b or when it is greater than V.sub.c, the output level of the OR gate 34 becomes high. When the output of the OR gate 34 is high, an actuating switch signal is supplied to the selector switch 7. Thus, the selector switch 7 is actuated so that the drive circuit 8 is connected to the output of the differential amplifier 31 instead of the output signal of the control signal generating circuit 6. Hence, the speed of the motor 2 is loop controlled. This loop control is used when the motor 2 is being started, when a search mode is entered, or when controlled movement of the pickup 3 due to loss of the reproduced signal is to be prevented.
However, these conventional systems for controlling the rotary drive of a disk player require the use of an expensive divider of complicated circuit construction. Another problem is that, since the F/V converter is required to have a certain high degree of conversion precision, the overall system circuitry is complicated and expensive.